Prior art electro hydraulic control systems have utilized an electric circuit having a varying current output through an electric motor device such as an electric force motor which modulatingly positions a movable valve element such as a valve spool which is axially movable within a valve bore. The amount of axial movement of the valve spool is generally proportional to the amount of current of the electric circuit. Furthermore, such prior art devices modulate the current output of the control circuit by input means which in the simplest form can consist of a manually positioned control handle. Incremental movement of the control handle proportionally controls the current output of the control circuit which in turn proportionally controls the axial position of the valve spool. One such example in the prior art is the MCH 100 control handle sold by Honeywell Corporation.
The incremental movement of the prior art positioning devices along with their electric circuitry do not compensate for the movable valve element "dead zone" mentioned above. Therefore, the initial movement of the positioning means from a zero current output position causes an increase in current flow to the electric force motor which in turn starts to move the valve spool, but since the valve spool is in the dead zone, this does not immediately initiate hydraulic flow through the servo valve.